CN111040058B

CN111040058B - Process for producing aqueous polytetrafluoroethylene dispersion

Info

Publication number: CN111040058B
Application number: CN201911257383.XA
Authority: CN
Inventors: 难波义典
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2012-11-30
Filing date: 2013-12-02
Publication date: 2022-10-25
Anticipated expiration: 2033-12-02
Also published as: EP2918613A1; EP2918613A4; JP6308949B2; CN104884476A; WO2014084397A1; JP6156543B2; CN111040058A; JP2016130328A; JPWO2014084397A1; US20150299341A1; US9574020B2; EP2918613B1

Abstract

The invention provides a method for producing an aqueous polytetrafluoroethylene dispersion, which can produce an aqueous fluoropolymer dispersion having a very small particle size and excellent dispersion stability without using a long-chain fluorosurfactant. The present invention relates to a method for producing an aqueous fluoropolymer dispersion, which comprises polymerizing a fluoromonomer in an aqueous medium in the presence of a fluorinated surfactant having a LogPOW of 3.4 or less and a polymerization initiator, wherein the aqueous dispersion contains at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene and melt-processable fluororesins (excluding polytetrafluoroethylene), and wherein the amount of the fluorinated surfactant in the aqueous medium is 4600ppm to 500000ppm.

Description

Process for producing aqueous polytetrafluoroethylene dispersion

The application is a divisional application, the Chinese national application number of the original application is 201380062185.2, the application date is 2013, 12 and 2, and the invention name is 'a method for preparing a polytetrafluoroethylene aqueous dispersion'.

Technical Field

The present invention relates to a method for producing an aqueous polytetrafluoroethylene dispersion.

Background

The aqueous fluororesin dispersion is usually produced by emulsion-polymerizing a fluorine-containing monomer in the presence of a fluorine-containing surfactant. As the fluorosurfactant, a long-chain fluorosurfactant such as perfluorooctanoic acid or a salt thereof has been conventionally used.

However, patent document 1 discloses the following: since ammonium perfluorooctanoate does not exist in nature and is a substance that is difficult to decompose, it is proposed from the environmental viewpoint to suppress the discharge of ammonium perfluorooctanoate; further, it is pointed out that ammonium perfluorooctanoate has high bioaccumulation properties.

Accordingly, patent document 1 proposes an aqueous polytetrafluoroethylene emulsion characterized in that, when tetrafluoroethylene is emulsion-polymerized alone or together with other copolymerizable monomers in an aqueous medium, 1500 to 20000ppm of the emulsion is used based on the final polytetrafluoroethylene yield

General formula (1): XCF ₂ CF ₂ (O) _m CF ₂ CF ₂ OCF ₂ COOA

(wherein X is a hydrogen atom or a fluorine atom, and A is a hydrogen atom, an alkali metal or NH ₄ M is an integer of 0 to 1) to obtain the aqueous polytetrafluoroethylene emulsion.

Patent document 2 describes an aqueous dispersion of low molecular weight polytetrafluoroethylene produced by a method for producing low molecular weight polytetrafluoroethylene, which is characterized by carrying out emulsion polymerization of tetrafluoroethylene or tetrafluoroethylene and a modifying monomer copolymerizable with the tetrafluoroethylene in an aqueous medium in the presence of a reactive compound having a functional group reactive in radical polymerization and a hydrophilic group, and in an amount exceeding 10ppm relative to the aqueous medium, and a chain transfer agent.

Patent document 3 describes an aqueous dispersion of fluoropolymer particles produced by a method for producing an aqueous dispersion of fluoropolymer particles, the method comprising the steps of: a step of providing dispersed fine particles of a fluorinated ionomer in an aqueous polymerization medium; and a step of polymerizing at least one fluorinated monomer in the presence of the dispersed fine particles of the fluorinated ionomer and an initiator in the aqueous polymerization medium to form an aqueous dispersion of particles of the fluoropolymer.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2007/046345 pamphlet

Patent document 2: japanese laid-open patent publication No. 2010-180364

Patent document 3: japanese Kokai publication Hei 2012-513530

Disclosure of Invention

Problems to be solved by the invention

In the prior art, when a fluorine-containing monomer is polymerized with a fluorine-containing surfactant different from a long-chain fluorine-containing surfactant, the particle size of the obtained fluororesin particles tends to be large. Further, the dispersion stability tends to be lowered, and there is a problem that the polymer adheres to a paddle during polymerization. In particular, it is not easy to obtain an aqueous fluoropolymer dispersion having a sufficiently small particle size and excellent dispersion stability.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a method for producing an aqueous fluoropolymer dispersion having an extremely small particle size and excellent dispersion stability without using a long-chain fluorosurfactant.

Means for solving the problems

The present inventors have conducted various studies on a method for producing an aqueous dispersion containing at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene and melt-processable fluororesins (excluding polytetrafluoroethylene) by polymerizing a fluorinated monomer in an aqueous medium in the presence of a fluorosurfactant and a polymerization initiator. And found that: the present inventors have completed the present invention by using a large amount of a fluorosurfactant having LogPOW in a specific range in the above polymerization, and thus producing an aqueous dispersion containing fluoropolymer particles having an extremely small volume average particle diameter without using a long-chain fluorosurfactant which has been conventionally used.

That is, the present invention relates to a method for producing an aqueous fluoropolymer dispersion, which comprises polymerizing a fluoromonomer in an aqueous medium in the presence of a fluorinated surfactant having a LogPOW of 3.4 or less and a polymerization initiator, wherein the aqueous dispersion contains at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene and melt-processable fluororesins (excluding polytetrafluoroethylene), and wherein the amount of the fluorinated surfactant in the aqueous medium corresponds to 4600ppm to 500000ppm.

The fluorosurfactant is preferably represented by the following general formula (1)

X-(CF ₂ ) _m1 -Y (1)

(wherein X represents H or F, m1 represents an integer of 3 to 5, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ (M represents H or NH) ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms)).

Preferably in the following general formula (2)

X-(CF ₂ ) _m2 -Y (2)

(wherein X represents H or F, m2 represents an integer of 6 or more, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ (M represents H or NH) ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms)) in the absence of a fluorine-containing compound.

The fluoropolymer is preferably a particle having a volume average particle diameter of 0.1nm or more and less than 20 nm.

The polymerization initiator is preferably at least one selected from the group consisting of persulfates and organic peroxides.

The amount of the polymerization initiator is preferably 1ppm to 5000ppm in the aqueous medium.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the method for producing an aqueous fluoropolymer dispersion of the present invention, an aqueous dispersion containing fluoropolymer particles having an extremely small particle diameter and having excellent dispersion stability can be produced without using a long-chain fluorosurfactant.

Detailed Description

Before the present invention is explained in detail, some terms used in the present specification are defined or explained.

In the present specification, the fluororesin means a partially crystalline fluoropolymer, and is not a fluororubber but a fluoroplastic. The fluororesin may have a melting point, may have thermoplasticity, and may have melt processability or non-melt processability.

In the present specification, melt processability means that a polymer is melted and processed by using existing processing equipment such as an extruder and an injection molding machine. Therefore, the melt flow rate of the melt-processable fluororesin is usually 0.01g/10 min to 500g/10 min as measured by the measurement method described later.

In the present specification, the perfluoro resin means a resin composed of a perfluoro polymer in which all monovalent atoms bonded to carbon atoms constituting the main chain of the polymer are fluorine atoms. However, a group such as an alkyl group, a fluoroalkyl group, an alkoxy group, or a fluoroalkoxy group may be bonded to a carbon atom constituting the main chain of the polymer, in addition to a monovalent atom (fluorine atom). The fluorine atoms bonded to the carbon atoms constituting the main chain of the polymer may be replaced by several chlorine atoms. Other atoms than fluorine atoms may be present at the polymer terminal groups, i.e., the groups that terminate the polymer chain. The polymer terminal groups are mostly groups derived from a polymerization initiator or a chain transfer agent used for polymerization.

In the present specification, the fluororubber means an amorphous fluoropolymer. The "amorphous state" means a case where the size of a melting peak (. DELTA.H) appearing in differential scanning calorimetry [ DSC ] (temperature rising rate of 10 ℃ C./min) or differential thermal analysis [ DTA ] (temperature rising rate of 10 ℃ C./min) of the fluoropolymer is 4.5J/g or less. Fluororubbers exhibit elastomeric properties by crosslinking. The elastomer properties refer to the following properties: the polymer can be stretched and the original length can be maintained when the force required to stretch the polymer has been inapplicable.

In the present specification, the perfluoromonomer means a monomer having no carbon atom-hydrogen atom bond in the molecule. The above-mentioned perfluoromonomer may be a monomer in which some of the fluorine atoms bonded to carbon atoms other than carbon atoms and fluorine atoms are substituted with chlorine atoms, or a monomer having nitrogen atoms, oxygen atoms and sulfur atoms other than carbon atoms. The perfluoromonomer is preferably a monomer in which all hydrogen atoms are replaced by fluorine atoms. The perfluoro monomer does not contain a monomer that provides a crosslinking site.

The monomer providing the crosslinking site is a monomer having a crosslinkable group (vulcanization site monomer) for providing the crosslinking site for forming the crosslink to the fluoropolymer by the curing agent.

In the present specification, the polytetrafluoroethylene [ PTFE ] is preferably a fluoropolymer having a tetrafluoroethylene content of 99 mol% or more based on the total polymerized units.

In the present specification, the fluorine resins (excluding polytetrafluoroethylene) are each preferably a fluorine-containing polymer having a content of tetrafluoroethylene of less than 99 mol% with respect to the total polymerized units.

In the present specification, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer.

Next, the present invention will be specifically described.

In the method for producing an aqueous fluoropolymer dispersion of the present invention, a fluorinated monomer is polymerized in an aqueous medium in the presence of a fluorinated surfactant having a LogPOW of 3.4 or less and a polymerization initiator, thereby producing an aqueous dispersion containing at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene [ PTFE ] and melt-processable fluororesins (excluding polytetrafluoroethylene).

The amount of the fluorinated surfactant used in the production method of the present invention is an amount corresponding to 4600ppm to 500000ppm in the aqueous medium. If the amount of the fluorosurfactant used is too small, an aqueous dispersion containing fluoropolymer particles having a small volume average particle diameter cannot be obtained; if the amount is too large, the effect corresponding to the amount cannot be obtained, and it is economically disadvantageous. The amount of the fluorinated surfactant to be used is preferably 18,000ppm or more, more preferably 20,000ppm or more, still more preferably 23,000ppm or more, particularly preferably 38,000ppm or more, preferably 400,000ppm or less, more preferably 300,000ppm or less.

The fluorosurfactant has a LogPOW of 3.4 or less. The LogPOW is a partition coefficient between 1-octanol and water, and is represented by LogP [ in the formula, P represents a ratio of a fluorine-containing surfactant concentration in octanol/a fluorine-containing surfactant concentration in water when a mixed solution of octanol/water (1). The LogPOW is preferably 1.5 or more, and is preferably 3.0 or less, more preferably 2.8 or less, from the viewpoint of easy removal from the fluoropolymer.

The LogPOWThe following was calculated: in the column: TOSOH ODS-120T column (. Phi.4.6 mm. Times.250 mm), eluent: acetonitrile/0.6 mass% HClO ₄ Water =1/1 (vol/vol%), flow rate: 1.0 ml/min, sample size: 300. Mu.L, column temperature: detection light at 40 ℃: the standard substances (heptanoic acid, octanoic acid, nonanoic acid and decanoic acid) having known octanol/water partition coefficients were subjected to HPLC under UV210nm to prepare calibration curves of the respective elution times and the known octanol/water partition coefficients, and the LogPOW was calculated from the HPLC elution times of the sample solutions based on the calibration curves.

As the fluorinated surfactant having a LogPOW of 3.4 or less, a fluorinated anionic surfactant is preferable, and examples thereof include fluorinated surfactants described in U.S. patent application publication No. 2007/0015864, U.S. patent application publication No. 2007/0015865, U.S. patent application publication No. 2007/0015866, U.S. patent application publication No. 2007/0276103, U.S. patent application publication No. 2007/0117914, U.S. patent application publication No. 2007/142541, U.S. patent application publication No. 2008/0015319, U.S. patent No. 3250808, U.S. patent No. 3271341, japanese patent application laid-open No. 2003-119204, international publication No. 2005/042593 pamphlet, pamphlet international publication No. 2008/060461, international publication No. 2007/046377, pamphlet international 2007/119526, international publication No. wo 2007/046482, pamphlet 2007/0445, and the like.

The fluorosurfactant having a LogPOW of 3.4 or less is preferably an anionic surfactant.

The anionic surfactant is preferably a carboxylic surfactant, a sulfonic surfactant, or the like, and examples of the surfactant include a surfactant composed of a perfluorocarboxylic acid (I) represented by the following general formula (I), an ω -H perfluorocarboxylic acid (II) represented by the following general formula (II), a perfluoropolyether carboxylic acid (III) represented by the following general formula (III), a perfluoroalkylalkylcarboxylic acid (IV) represented by the following general formula (IV), a perfluoroalkoxyfluorocarboxylic acid (V) represented by the following general formula (V), a perfluoroalkylalkylsulfonic acid (VI) represented by the following general formula (VI), and/or a perfluoroalkylalkylsulfonic acid (VII) represented by the following general formula (VII).

The above perfluorocarboxylic acid (I) is represented by the following general formula (I)

F(CF ₂ ) _n1 COOM (I)

(wherein n1 is an integer of 3 to 6, and M is H or NH) ₄ Or an alkali metal element).

In the general formula (I), a preferable lower limit of n1 is 4 in view of stability of the polymerization reaction. Further, M is preferably NH, because it is less likely to remain during processing of the resulting aqueous fluoropolymer dispersion ₄ 。

As the above perfluorocarboxylic acid (I), for example, F (CF) is preferable ₂ ) ₆ COOM、F(CF ₂ ) ₅ COOM、F(CF ₂ ) ₄ COOM (wherein M is defined above in the formulae), and the like.

The omega-H perfluorocarboxylic acid (II) is represented by the following general formula (II)

H(CF ₂ ) _n2 COOM (II)

(wherein n2 is an integer of 4 to 8, and M is as defined above).

In the general formula (II), a preferable upper limit of n2 is 6 in view of stability of the polymerization reaction. Further, in view of being less likely to remain during processing of the aqueous fluoropolymer dispersion obtained, M is preferably NH ₄ 。

As the above-mentioned omega-H perfluorocarboxylic acid (II), for example, H (CF) is preferred ₂ ) ₈ COOM、H(CF ₂ ) ₇ COOM、H(CF ₂ ) ₆ COOM、H(CF ₂ ) ₅ COOM、H(CF ₂ ) ₄ COOM (in the formulae, M is defined above), and the like.

The above perfluoropolyether carboxylic acid (III) is represented by the following general formula (III)

Rf ¹ -O-(CF(CF ₃ )CF ₂ O) _n3 CF(CF ₃ )COOM (III)

(wherein, rf ¹ Is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above) As indicated.

In the general formula (III), the Rf is preferable from the viewpoint of stability during polymerization ¹ Preferably a perfluoroalkyl group having 4 or less carbon atoms, n3 is preferably 0 or 1, and M is preferably NH from the viewpoint of being less likely to remain during the processing of the resulting aqueous fluoropolymer dispersion ₄ 。

The perfluoropolyether carboxylic acid (III) is preferably, for example

C ₄ F ₉ OCF(CF ₃ )COOM、C ₃ F ₇ OCF(CF ₃ )COOM、

C ₂ F ₅ OCF(CF ₃ )COOM、CF ₃ OCF(CF ₃ )COOM、

CF ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOM

(wherein M is a substance defined above) and the like, and is more preferably used from the viewpoint of good stability and removal efficiency at the time of polymerization

CF ₃ OCF(CF ₃ )COOM、CF ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOM

(wherein M is a substance defined as above) and the like.

The above perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV)

Rf ² (CH ₂ ) _n4 Rf ³ COOM (IV)

(wherein Rf ² Is a perfluoroalkyl group having 1 to 5 carbon atoms, rf ³ A linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above).

In the above general formula (IV), the above Rf ² A perfluoroalkyl group having 2 or more carbon atoms or a perfluoroalkyl group having 4 or less carbon atoms is preferable. Rf above ³ It is preferably a perfluoroalkylene group having 1 or 2 carbon atoms, more preferably- (CF) ₂ ) -or-CF (CF) ₃ ) -. N4 is preferably 1 or 2, more preferably 1. In view of being less likely to remain during processing of the aqueous fluoropolymer dispersion obtained, M is preferablyNH ₄ 。

As the above perfluoroalkyl alkylene carboxylic acid (IV), for example, preferred is

C ₄ F ₉ CH ₂ CF ₂ COOM、C ₃ F ₇ CH ₂ CF ₂ COOM、

C ₂ F ₅ CH ₂ CF ₂ COOM、C ₄ F ₉ CH ₂ CF(CF ₃ )COOM、

C ₃ F ₇ CH ₂ CF(CF ₃ )COOM、C ₂ F ₅ CH ₂ CF(CF ₃ )COOM、

C ₄ F ₉ CH ₂ CH ₂ CF ₂ COOM、C ₃ F ₇ CH ₂ CH ₂ CF ₂ COOM、

C ₂ F ₅ CH ₂ CH ₂ CF ₂ COOM

(in each formula, M is a substance defined as above) and the like.

The perfluoroalkoxy fluorocarboxylic acid (V) is represented by the following general formula (V)

Rf ⁴ -O-CY ¹ Y ² CF ₂ -COOM (V)

(wherein Rf ⁴ Is a perfluoroalkyl group having 1 to 5 carbon atoms, Y ¹ And Y ² Identical or different, H or F, M being a substance as defined above).

In the general formula (V), the Rf is preferable from the viewpoint of polymerization stability ⁴ A perfluoroalkyl group having 1 to 3 carbon atoms is preferable, and a perfluoroalkyl group having 3 carbon atoms is more preferable. In view of being less likely to remain during processing of the resulting aqueous fluoropolymer dispersion, M is preferably NH ₄ 。

As the above-mentioned perfluoroalkoxy fluorocarboxylic acid (V), preferred is

C ₃ F ₇ OCH ₂ CF ₂ COOM、C ₃ F ₇ OCHFCF ₂ COOM、

C ₃ F ₇ OCF ₂ CF ₂ COOM

(in each formula, M is a substance defined as above) and the like.

The above perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI)

F(CF ₂ ) _n5 SO ₃ M (VI)

(wherein n5 is an integer of 3 to 6, and M is as defined above).

In the general formula (VI), n5 is preferably an integer of 4 or 5 from the viewpoint of polymerization stability, and M is preferably NH from the viewpoint of being less likely to remain during processing of the resulting aqueous fluoropolymer dispersion ₄ 。

As the above-mentioned perfluoroalkylsulfonic acid (VI), for example, preferred is

F(CF ₂ ) ₅ SO ₃ M、F(CF ₂ ) ₅ SO ₃ M

(in each formula, M is a substance defined as above) and the like.

The above perfluoroalkyl alkylene sulfonic acid (VII) is represented by the following general formula (VII)

Rf ⁵ (CH ₂ ) _n6 SO ₃ M (VII)

(wherein Rf ⁵ A perfluoroalkyl group of 1 to 5, n6 is an integer of 1 to 3, and M is a substance defined as above).

In the above general formula (VII), rf ⁵ The perfluoroalkyl group preferably has 1 to 3 carbon atoms, and more preferably has 3 carbon atoms. N6 is preferably 1 or 2, more preferably 1. In view of being less likely to remain during processing of the resulting aqueous fluoropolymer dispersion, M is preferably NH ₄ 。

As the above-mentioned perfluoroalkylalkylene sulfonic acid (VII), for example, preferred is

C ₃ F ₇ CH ₂ SO ₃ M

(wherein M is defined as above) and the like.

The fluorinated surfactant having a LogPOW of 3.4 or less is preferably one selected from the group consisting of the following general formula (1)

X-(CF ₂ ) _m1 -Y (1)

(formula (II)Wherein X represents H or F, m1 represents an integer of 3 to 5, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ (M represents H or NH) ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms)), a ω -H perfluorocarboxylic acid (II) represented by the general formula (II), a perfluoropolyether carboxylic acid (III) represented by the general formula (III), a perfluoroalkylalkylene carboxylic acid (IV) represented by the general formula (IV), a perfluoroalkoxy fluorocarboxylic acid (V) represented by the general formula (V), and a perfluoroalkylalkylene sulfonic acid (VII) represented by the general formula (VII).

The fluorosurfactant having a LogPOW of 3.4 or less is more preferably selected from the group consisting of those represented by the following general formula (1)

X-(CF ₂ ) _m1 -Y (1)

(wherein X represents H or F, m1 represents an integer of 3 to 5, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ (M represents H or NH) ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms)), or a fluorine-containing compound represented by the following general formula (3)

CF ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOX (3)

(wherein X represents a hydrogen atom or NH) ₄ Or an alkali metal atom) and the following general formula (4)

CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COOX (4)

(wherein X represents a hydrogen atom or NH) ₄ Or an alkali metal atom) of a fluorine-containing compound.

Further, as the fluorosurfactant having a LogPOW of 3.4 or less, the following general formula (1) is more preferable

X-(CF ₂ ) _m1 -Y (1)

Examples of the fluorine-containing monomer include fluoroolefins, preferably fluoroolefins having 2 to 10 carbon atoms; a cyclic fluorinated monomer; formula CQ ₂ ＝CQOR ¹ Or CQ ₂ ＝CQOR ² OR ³ (Q is H or F, R) ¹ And R ³ Is an alkyl group having 1 to 8 carbon atoms in which some or all of the hydrogen atoms are replaced by fluorine atoms, R ² An alkylene group having 1 to 8 carbon atoms wherein a part or all of the hydrogen atoms are replaced with fluorine atoms); a fluorine-containing olefin having a nitrile group; fluorine-containing vinyl ethers having a nitrile group, and the like.

More specifically, the fluorine-containing monomer is preferably selected from the group consisting of tetrafluoroethylene [ TFE ]]Hexafluoropropylene [ HFP ]]Chlorotrifluoroethylene [ CTFE ]]Vinyl fluoride, vinylidene fluoride [ VDF ]]Trifluoroethylene, hexafluoroisobutylene, CH ₂ ＝CZ ¹ (CF ₂ ) _n Z ² (in the formula, Z ¹ Is H or F, Z ² H, F or Cl, n is an integer of 1 to 10), CF ₂ ＝CF-ORf ⁶ (wherein Rf ⁶ Represents a C1-C8 perfluoroalkyl group) [ PAVE ]]、CF ₂ ＝CF-O-CH ₂ -Rf ⁷ (wherein Rf ⁷ Is a perfluoroalkyl group having 1 to 5 carbon atoms), perfluoro-2, 2-dimethyl-1, 3-dioxole [ PDD ]]And perfluoro-2-methylene-4-methyl-1, 3-dioxolane [ PMD]At least one of the group consisting of.

As CH ₂ ＝CZ ¹ (CF ₂ ) _n Z ² Examples of the monomer include CH ₂ ＝CFCF ₃ 、CH ₂ ＝CH-C ₄ F ₉ 、CH ₂ ＝CH-C ₆ F ₁₃ 、CH ₂ ＝CF-C ₃ F ₆ H, and the like.

As CF ₂ ＝CF-ORf ⁶ Examples of the perfluoro (alkyl vinyl ether) include CF ₂ ＝CF-OCF ₃ 、CF ₂ ＝CF-OCF ₂ CF ₃ And CF ₂ ＝CF-OCF ₂ CF ₂ CF ₃ 。

In addition to the above-mentioned fluorine-containing monomer, a non-fluorine-containing monomer may be polymerized. Examples of the non-fluorine-containing monomer include hydrocarbon monomers reactive with the fluorine-containing monomer. Examples of the hydrocarbon monomer include olefins such as ethylene, propylene, butylene, and isobutylene; alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, and cyclohexyl vinyl ether; vinyl esters such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl isobutyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl versatate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl benzoate, vinyl p-tert-butylbenzoate, vinyl cyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate, vinyl hydroxyacetate, vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxyisobutyrate, and vinyl hydroxycyclohexanecarboxylate; alkylallyl ethers such as ethylallyl ether, propylallyl ether, butylallyl ether, isobutylallyl ether, and cyclohexylallyl ether; and alkylallyl esters such as ethylallyl ester, propylallyl ester, butylallyl ester, isobutylallyl ester, and cyclohexylallyl ester.

The non-fluorine-containing monomer may be a hydrocarbon monomer having a functional group. Examples of the functional group-containing hydrocarbon monomer include hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether, and hydroxycyclohexyl vinyl ether; non-fluorine-containing monomers having a glycidyl group such as glycidyl vinyl ether and glycidyl allyl ether; non-fluorine-containing monomers having an amino group such as aminoalkyl vinyl ether and aminoalkyl allyl ether; non-fluorine-containing monomers having amide groups such as (meth) acrylamide and methylolacrylamide; bromine-containing olefins, iodine-containing olefins, bromine-containing vinyl ethers, iodine-containing vinyl ethers; non-fluorine-containing monomers having a nitrile group, and the like.

By polymerizing the above-mentioned fluorine-containing monomer, an aqueous dispersion containing at least one fluorine-containing polymer selected from the group consisting of PTFE and a melt-processable fluororesin (in which PTFE is not included) can be obtained.

The PTFE may be homopolyptfe or modified PTFE. The modified PTFE comprises TFE units and modifying monomer units based on a modifying monomer copolymerizable with TFE. The PTFE may be high-molecular-weight PTFE having non-melt-processability and fibrillating properties, or low-molecular-weight PTFE having melt-processability but not fibrillating properties.

The modifying monomer is not particularly limited as long as it is a monomer copolymerizable with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene [ HFP ]; chlorofluoroalkenes such as chlorotrifluoroethylene [ CTFE ]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [ VDF ]; a perfluorovinyl ether; a perfluoroalkylethylene; ethylene; fluorine-containing vinyl ethers having a nitrile group, and the like. One or two or more modifying monomers may be used.

The perfluorovinyl ether is not particularly limited, and examples thereof include the following general formula (5)

CF ₂ ＝CF-ORf ⁸ (5)

(wherein, rf ⁸ A perfluoroorganic group) and the like. In the present specification, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The aforementioned perfluoroorganic group may have an ether oxygen.

Examples of the perfluorovinyl ether include Rf in the general formula (5) ⁸ Perfluoro (alkyl vinyl ether) [ PAVE ] representing C1-10 perfluoroalkyl group]. Of the above perfluoroalkyl groupsThe number of carbon atoms is preferably 1 to 5.

Examples of the perfluoroalkyl group in PAVE include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, etc., and perfluoropropyl vinyl ether [ PPVE ] in which the perfluoroalkyl group is perfluoropropyl group is preferable.

Further examples of the above-mentioned perfluorovinyl ether include Rf in the above-mentioned general formula (5) ⁸ Is a perfluoro (alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf ⁸ Is of the formula:

(wherein m represents 0 or an integer of 1 to 4), and Rf ⁸ Is of the formula:

(wherein n represents an integer of 1 to 4), and the like.

The perfluoroalkyl ethylene is not particularly limited, and examples thereof include perfluorobutyl ethylene (PFBE) and perfluorohexyl ethylene (PFHE).

As the fluorine-containing vinyl ether having a nitrile group, CF is more preferable ₂ ＝CFORf ⁹ CN (in the formula, rf) ⁹ An alkylene group having 2 to 7 carbon atoms which may have an oxygen atom inserted between two carbon atoms).

The modified monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PPVE, PFBE, and ethylene. More preferably at least one monomer selected from the group consisting of HFP and CTFE.

The modified monomer unit in the modified PTFE is preferably in the range of 0.001 mol% to 2 mol%, and more preferably in the range of 0.001 mol% to less than 1 mol%.

In the present specification, the content of each monomer constituting PTFE can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer.

The PTFE obtained by the production method of the present invention preferably has a Melt Viscosity (MV) of 1.0 × 10Pa · S or more, more preferably 1.0 × 10Pa · S ² Pa · S or more, more preferably 1.0X 10 ³ Pa · S or more.

The above melt viscosity can be measured as follows: the measurement was carried out by holding a 2g sample heated at a measurement temperature (380 ℃) for 5 minutes at the above temperature under a load of 0.7MPa using a flow tester (manufactured by Shimadzu corporation) and a mold of 2 φ -8L according to ASTM D1238.

The melting point of PTFE obtained by the production method of the present invention is preferably 324 to 360 ℃.

In the present specification, the melting point is a temperature corresponding to the maximum value in the heat of fusion curve when the temperature is raised at a rate of 10 ℃/minute by a differential scanning calorimeter [ DSC ].

The melt-processable fluororesin is preferably at least one fluororesin selected from the group consisting of TFE/PAVE copolymer [ PFA ], TFE/HFP copolymer [ FEP ], ethylene [ Et ]/TFE copolymer [ ETFE ], et/TFE/HFP copolymer, polychlorotrifluoroethylene [ PCTFE ], CTFE/TFE copolymer, et/CTFE copolymer, and PVF, and more preferably at least one perfluororesin selected from the group consisting of PFA and FEP.

The PFA is not particularly limited, but is preferably a copolymer having a molar ratio of TFE units to PAVE units (TFE units/PAVE units) of 70/30 or more and less than 99/1. More preferably 70/30 to 98.9/1.1, and still more preferably 80/20 to 98.9/1.1. When the amount of the TFE unit is too small, mechanical properties tend to be deteriorated; if the amount is too large, the melting point becomes too high, and moldability tends to be lowered. The PFA is preferably a copolymer having 0.1 to 10 mol% of a monomer unit derived from a monomer copolymerizable with TFE and PAVE, and 90 to 99.9 mol% of the total of TFE unit and PAVE unit. Examples of the monomer copolymerizable with TFE and PAVE include HFP and CZ ³ Z ⁴ ＝CZ ⁵ (CF ₂ ) _n Z ⁶ (in the formula, Z ³ 、Z ⁴ And Z ⁵ Identical or different, represents a hydrogen atom or a fluorine atom, Z ⁶ Represents a hydrogen atom, a fluorine atom or a chlorine atom, and n represents an integer of 2 to 10), and CF ₂ ＝CF-OCH ₂ -Rf ⁷ (wherein, rf ⁷ A perfluoroalkyl group having 1 to 5 carbon atoms), and the like.

The melting point of PFA is lower than that of PTFE, preferably 180 to 324 ℃, more preferably 230 to 320 ℃, and still more preferably 280 to 320 ℃.

The PFA preferably has a Melt Flow Rate (MFR) of 1g/10 min to 500g/10 min.

In the present specification, MFR is measured at a measurement temperature (e.g., 372 ℃ in the case of PFA or FEP and 297 ℃ in the case of ETFE) and a load (e.g., 5kg in the case of PFA, FEP and ETFE) determined in accordance with the kind of fluoropolymer, using values obtained by the method according to ASTM D1238.

The FEP is not particularly limited, but a copolymer having a molar ratio of TFE units to HFP units (TFE unit/HFP unit) of 70/30 or more and less than 99/1 is preferable. More preferably 70/30 to 98.9/1.1, and still more preferably 80/20 to 98.9/1.1. When the amount of the TFE unit is too small, mechanical properties tend to be deteriorated; if too much, the melting point becomes too high, and moldability tends to deteriorate. The FEP is also preferably a copolymer in which the monomer unit derived from a monomer copolymerizable with TFE and HFP is 0.1 to 10 mol% and the total of TFE and HFP units is 90 to 99.9 mol%. As the monomer copolymerizable with TFE and HFP, PAVE, an alkyl perfluorovinyl ether derivative, and the like can be given.

The melting point of FEP is lower than the melting point of PTFE, preferably 150 to less than 324 ℃, more preferably 200 to 320 ℃, and still more preferably 240 to 320 ℃.

The preferred MFR of the FEP is 1g/10 min to 500g/10 min.

As ETFE, a copolymer in which the molar ratio of TFE units to ethylene units (TFE units/ethylene units) is 20/80 to 90/10 is preferable. More preferably, the molar ratio is 37/63 to 85/15, still more preferably 38/62 to 80/20. ETFE may also be a copolymer composed of TFE, ethylene, and a monomer copolymerizable with TFE and ethylene. As the copolymerizable monomer, the following formula may be mentioned

CH ₂ ＝CX ⁵ Rf ³ 、CF ₂ ＝CFRf ³ 、CF ₂ ＝CFORf ³ 、CH ₂ ＝C(Rf ³ ) ₂

(in the formula, X ⁵ Represents a hydrogen atom or a fluorine atom, rf ³ Represents a fluoroalkyl group which may contain an ether bond), wherein CF is preferred ₂ ＝CFRf ³ 、CF ₂ ＝CFORf ³ And CH ₂ ＝CX ⁵ Rf ³ The fluorine-containing vinyl monomer is more preferably HFP or CF ₂ ＝CF-ORf ⁴ (wherein, rf ⁴ Represents a C1-5 perfluoroalkyl group), and Rf ³ CH being a fluoroalkyl group having 1 to 8 carbon atoms ₂ ＝CX ⁵ Rf ³ The fluorine-containing vinyl monomer is represented. Further, as the monomer copolymerizable with TFE and ethylene, an aliphatic unsaturated carboxylic acid such as itaconic acid or itaconic anhydride may be used. The amount of the monomer copolymerizable with TFE and ethylene is preferably 0.1 to 10 mol%, more preferably 0.1 to 5 mol%, and particularly preferably 0.2 to 4 mol% based on the fluoropolymer.

The melting point of ETFE is lower than that of PTFE, preferably 140 to less than 324 ℃, more preferably 160 to 320 ℃, and still more preferably 195 to 320 ℃.

The ETFE preferably has an MFR of 1g/10 min to 500g/10 min.

The content of each monomer unit in the copolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer.

The fluoropolymer is preferably a particle having a volume average particle diameter of 0.1nm or more and less than 20 nm. When the volume average particle diameter is in the above range, the particles can be dispersed extremely finely in the substrate, and therefore, the sliding property and the texture of the coating film surface can be further improved. In addition, if the fluoropolymer particles having a volume average particle diameter in the above range are subjected to multi-stage polymerization, an aqueous dispersion containing fluororesin particles having an extremely small particle diameter can be produced. If the volume average particle diameter is too large, an aqueous dispersion containing fluororesin particles having an extremely large particle diameter is formed, and thus, the reaction stability may be poor and an unexpected aggregate may be generated during the polymerization. Further, when fluoropolymer particles having an excessively large volume average particle size are subjected to multi-stage polymerization, it is not possible to produce an aqueous dispersion having excellent dispersion stability containing fluororesin particles having an extremely small particle size. Fluoropolymer particles having a volume average particle size of less than 0.1nm are not easily produced. The volume average particle diameter of the fluoropolymer particles is more preferably 0.5nm or more, particularly preferably 1.0nm or more, preferably 15nm or less, more preferably 10nm or less, and particularly preferably 5nm or less.

The volume average particle diameter was measured by a dynamic light scattering method. Are the values measured as follows: an aqueous fluoropolymer dispersion was prepared so that the concentration of the fluoropolymer as a solid matter was adjusted to 1.0% by mass, and the concentration was measured at 25 ℃ and 70 times in total by using ELSZ-1000S (manufactured by Otsuka Denshi Co., ltd.). The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPas. The volume average particle diameter is an average particle diameter in a state of being dispersed as primary particles.

The fluoropolymer is preferably not a fluorinated ionomer because it is difficult to apply the fluoropolymer to the use of an aqueous fluoropolymer dispersion described later.

The fluoropolymer preferably has an Equivalent Weight (EW) of 6,000 or more. The Equivalent Weight (EW) is a dry weight per 1 equivalent of ion-exchange group, and the Equivalent Weight (EW) of the fluoropolymer is large meaning that almost no ionomer is contained in the monomers constituting the fluoropolymer. Although the fluoropolymer described above contains little ionomer, it surprisingly has a very small volume average particle size. The Equivalent Weight (EW) is more preferably 10,000 or more, and the upper limit is not particularly limited, and is preferably 50,000,000 or less.

In the method for producing an aqueous dispersion of fluoropolymer particles described in patent document 3, since dispersed fine particles of a fluorinated ionomer need to be formed in the first step, the heat resistance of the fluoropolymer finally obtained is also poor, and when the obtained fluoropolymer is heated, foaming or coloring may occur. In the production method of the present invention, the Equivalent Weight (EW) of the resulting fluoropolymer is 6,000 or more, and therefore the resulting fluoropolymer has excellent heat resistance.

The equivalent weight can be measured by the following method.

Hydrochloric acid or nitric acid is added to an aqueous dispersion containing a fluoropolymer to precipitate the fluoropolymer. The deposited fluoropolymer is washed with pure water until the washing liquid becomes neutral, and then dried by vacuum heating at 110 ℃ or lower until the water disappears. About 0.3g of the dried fluoropolymer was immersed in 30mL of a saturated aqueous NaCl solution at 25 ℃ and left to stand for 30 minutes with stirring. Next, the protons in the saturated NaCl aqueous solution were subjected to neutralization titration with a 0.01N sodium hydroxide aqueous solution using phenolphthalein as an indicator. The fluoropolymer obtained after neutralization in the state in which the counter ion of the ion exchange group was sodium ion was rinsed with pure water, and further vacuum-dried and weighed. The equivalent weight EW (g/eq) was determined by the following equation, assuming that the mass of sodium hydroxide required for neutralization was M (mmol) and the mass of the fluoropolymer whose counter ion of the ion exchange group was sodium ion was W (mg).

EW＝(W/M)－22

The polymerization initiator is not particularly limited as long as it can generate radicals in the above polymerization temperature range, and known oil-soluble and/or water-soluble polymerization initiators can be used. Further, the polymerization may be initiated in a redox manner in combination with a reducing agent or the like. The concentration of the polymerization initiator may be appropriately determined depending on the kind of the monomer, the molecular weight of the target polymer, and the reaction rate.

The polymerization initiator is preferably at least one selected from the group consisting of persulfates and organic peroxides. The polymerization initiator is excellent in dispersion stability in an aqueous dispersion of fluoropolymer particles, and therefore, examples thereof include water-soluble organic peroxides such as persulfates, e.g., ammonium persulfate and potassium persulfate, and succinyl peroxide and bisglutaric acid peroxide.

The amount of the polymerization initiator to be used is preferably 2ppm or more in the aqueous medium because the dispersion stability in the aqueous dispersion of the fluoropolymer particles is good.

The aqueous medium is a reaction medium for carrying out polymerization and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water, a non-fluorinated organic solvent such as an alcohol, an ether or a ketone, and/or a fluorinated organic solvent having a boiling point of 40 ℃ or lower.

The polymerization in the production method of the present invention may be carried out in the presence of a chain transfer agent. As the chain transfer agent, known chain transfer agents can be used, and examples thereof include saturated hydrocarbons such as methane, ethane, propane, butane and the like; halogenated hydrocarbons such as methyl chloride, methylene chloride and difluoroethane; alcohols such as methanol and ethanol; hydrogen; and the like, preferably in a gaseous state at normal temperature and pressure, more preferably ethane or propane.

The amount of the chain transfer agent to be used is usually 1 to 50,000ppm, preferably 1 to 20,000ppm based on the total amount of the fluoromonomer to be supplied.

The chain transfer agent may be added to the reaction vessel all at once before the start of polymerization, may be added in several portions during the polymerization, or may be continuously added during the polymerization.

The polymerization is preferably carried out at 10 to 95 ℃, more preferably at 30 ℃ or higher, and still more preferably at 90 ℃ or lower.

The polymerization is preferably carried out at 0.05MPaG to 3.9MPaG, more preferably at 0.1MPaG or more, and still more preferably at 3.0MPaG or less.

The above polymerization is carried out by: the polymerization is carried out by charging TFE and, if necessary, a modifying monomer into a polymerization reactor, stirring the contents of the reactor while maintaining the reactor at a specific polymerization temperature, and then adding a polymerization initiator to initiate the polymerization reaction. The aqueous medium, additives and the like may be charged into the reactor as necessary before the polymerization reaction starts. After the polymerization reaction is started, TFE, a modified monomer, a polymerization initiator, a chain transfer agent, and the like may be added according to the purpose.

By carrying out the above polymerization, an aqueous dispersion containing fluoropolymer particles can be produced. The solid content concentration of the obtained aqueous dispersion is approximately 1 to 40 mass%, preferably 5 to 30 mass%. Regarding the solid content concentration, 1g of the aqueous dispersion was dried in an air-blown dryer at 150 ℃ for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion was expressed as a percentage.

In the aqueous fluoropolymer dispersion of the present invention, the amount of the fluoropolymer particles sedimented as measured with respect to the aqueous fluoropolymer dispersion having a solid content concentration of 5.0 mass% of the fluoropolymer particles is preferably 10.0 mass% or less, more preferably 7.0 mass% or less, still more preferably 5.5 mass% or less, and particularly preferably 3.0 mass% or less. The lower limit is not particularly limited.

Here, the "amount of the fluoropolymer particles settled" can be measured, for example, by the following method. 30g of the aqueous fluoropolymer dispersion kept at 25 ℃ was charged into a dedicated vessel, and was kept at 5000rpm for 5 minutes by a centrifugal separator (himac CT 15D) manufactured by Hitachi engineering Co., ltd., equipped with an RT15A7 type rotor, to separate the dispersion into a sediment layer and an aqueous fluoropolymer dispersion layer. The aqueous fluoropolymer dispersion layer was taken out to determine the amount of solid content, and the amount of sediment was calculated from the difference between the amount of solid content and the amount of solid content in the aqueous fluoropolymer dispersion used. The amount of the sediment was measured as a ratio (% by mass) of the amount of the fluoropolymer contained in the aqueous fluoropolymer dispersion to be used. The lower the ratio, the more excellent the storage stability.

In the aqueous fluoropolymer dispersion of the present invention, the amount of fluoropolymer particles sieved as measured with respect to an aqueous fluoropolymer dispersion having a solid content concentration of fluoropolymer particles of 5.0 mass% is preferably 2.5 mass% or less, more preferably 2.0 mass% or less, still more preferably 1.8 mass% or less, and particularly preferably 1.3 mass% or less. The lower limit is not particularly limited.

Here, the "sieving amount of the fluoropolymer particles" is measured, for example, by the following method. 100g of an aqueous fluoropolymer dispersion kept at 65 ℃ was circulated for 2 hours at a discharge flow rate of 10L/hr by a quantitative liquid-feeding pump (RP-2000 type roller pump) made by Tokyo chemical instruments Co., ltd., equipped with a tube (Tygon tube) having an inner diameter of 4.76mm and an outer diameter of 7.94 mm. Thereafter, the amount of the sieve in the case of filtration using a 200-mesh SUS mesh was measured as the ratio (% by mass) of the amount of the fluoropolymer contained in the aqueous fluoropolymer dispersion to be used. A lower ratio indicates more excellent mechanical stability.

The polymerization in the production process of the present invention is preferably represented by the following general formula (2)

X-(CF ₂ ) _m2 -Y (2)

(wherein X represents H or F, m2 represents an integer of 6 or more, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ (M represents H or NH) ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms)) in the absence of a fluorine-containing compound. According to the production method of the present invention, an aqueous dispersion containing fluoropolymer particles having a sufficiently small volume average particle diameter can be produced without using such a conventional long-chain fluorinated surfactant.

The polymerization in the production method of the present invention is preferably emulsion polymerization. The polymerization in the production method of the present invention is preferably radical polymerization.

The aqueous fluoropolymer dispersion obtained by the production process of the present invention may be subjected to multistage polymerization. Since the aqueous fluoropolymer dispersion obtained by the production method of the present invention contains fluoropolymer particles having an extremely small particle size, an aqueous dispersion containing fluororesin particles having a core-shell structure in which the fluoropolymer particles are used as a core part and an extremely small particle size can be produced by subjecting the aqueous fluoropolymer dispersion to multi-stage polymerization.

Further, the fluoropolymer fine powder can be produced by performing the following steps: a step of precipitating the aqueous fluoropolymer dispersion obtained by the production method of the present invention; a step of washing the obtained precipitated particles; and a step of drying.

As the above-mentioned precipitation, washing and drying methods, conventionally known methods can be employed.

Further, an aqueous fluoropolymer dispersion containing no fluorosurfactant and having a high solid content concentration can be produced by a production method comprising the steps of: a step (I) in which the aqueous fluoropolymer dispersion obtained by the production method of the present invention is brought into contact with an anion exchange resin in the presence of a nonionic surfactant; and a step (II) of concentrating the aqueous dispersion obtained in the step (I) so that the concentration of the solid content in the aqueous dispersion is 30 to 70 mass% with respect to 100 mass% of the aqueous dispersion.

Regarding the solid content concentration of the concentrated aqueous fluoropolymer dispersion, 1g of the aqueous dispersion was dried in an air-blown dryer at 380 ℃ for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion was expressed as a percentage.

The step of contacting with the anion exchange resin can be carried out by a conventionally known method. The concentration method may be the above method.

The production method of the present invention preferably includes, after the step (I), a step of separating the aqueous fluoropolymer dispersion from the anion exchange resin to recover the aqueous fluoropolymer dispersion.

The nonionic surfactant is not particularly limited as long as it is composed of a non-fluorine-containing nonionic compound, and known ones can be used. Examples of the nonionic surfactant include ether type nonionic surfactants such as polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, and polyoxyethylene alkylene alkyl ethers; polyoxyethylene derivatives such as ethylene oxide/propylene oxide block copolymers; ester-type nonionic surfactants such as sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, and polyoxyethylene fatty acid esters; amine-based nonionic surfactants such as polyoxyethylene alkylamines and alkyl alkanolamides; and so on. They are all non-fluorinated nonionic surfactants.

Among the compounds constituting the nonionic surfactant, the hydrophobic group may be any of an alkylphenol group, a straight-chain alkyl group and a branched alkyl group, and a compound having no benzene ring such as a compound having no alkylphenol group in the structure is preferable.

Among the above nonionic surfactants, polyoxyethylene alkyl ethers are preferred. The polyoxyethylene alkyl ether is preferably a polyoxyethylene alkyl ether having a polyoxyethylene alkyl ether structure having an alkyl group having 10 to 20 carbon atoms, and more preferably a polyoxyethylene alkyl ether having an alkyl group having 10 to 15 carbon atoms. The alkyl group in the polyoxyethylene alkyl ether structure preferably has a branched structure.

Examples of commercially available products of the polyoxyethylene alkyl ether include Genapol X080 (product name, manufactured by Clariant), TERGITOL 9-S-15 (product name, manufactured by Clariant), noigen TDS-80 (product name, manufactured by first Industrial pharmaceutical Co., ltd.), and Leocol TD-90 (product name, manufactured by LION).

The aqueous fluoropolymer dispersion and the fluoropolymer fine powder obtained by the production method of the present invention can be suitably used as additives for modifying molding materials, inks, cosmetics, paints, greases, office automation equipment parts, toners, additives in plating solutions, and the like. Examples of the molding material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide.

The aqueous fluoropolymer dispersion obtained by the production method of the present invention and the fluoropolymer fine powder can be suitably used as additives for molding materials, for example, for improving non-tackiness and sliding properties of a transfer roll; improving the texture of engineering plastic molded products such as surface sheets of furniture, instrument panels of automobiles, and housings of household electrical appliances; applications for improving the sliding properties or wear resistance of mechanical parts capable of generating mechanical friction, such as light-duty bearings, gears, cams, push buttons for push-button phones, projectors, camera parts, and sliding materials; processing aids for engineering plastics, and the like.

The aqueous fluoropolymer dispersion obtained by the production process of the present invention and the fluoropolymer fine powder can be used as an additive for a coating material for the purpose of improving the sliding properties of a varnish or a coating material. The aqueous fluoropolymer dispersion and fluoropolymer fine powder of the present invention can be used as an additive for cosmetics for the purpose of improving the sliding properties of cosmetics such as foundation.

The aqueous fluoropolymer dispersion obtained by the production method of the present invention and the fluoropolymer fine powder are further suitable for applications of improving oil repellency or water repellency of wax or the like; the use of the grease or toner for improving the sliding property.

The aqueous fluoropolymer dispersion obtained by the production method of the present invention and the fluoropolymer fine powder can also be used as an electrode binder for a secondary battery or a fuel cell, a hardness adjuster for an electrode binder, a water repellent treatment agent for an electrode surface, and the like. In this application, the aqueous fluoropolymer dispersion is often more suitable than the fine fluoropolymer powder.

Examples

The present invention will be described with reference to examples, but the present invention is not limited to the examples.

The values of the examples were measured by the following methods.

(volume average particle diameter)

The measurement was performed by a dynamic light scattering method. An aqueous fluoropolymer dispersion was prepared so that the concentration of the fluoropolymer as a solid matter was adjusted to 1.0% by mass, and the concentration was measured at 25 ℃ and 70 times in total by using ELSZ-1000S (manufactured by Otsuka Denshi Co., ltd.). The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPas.

(melt viscosity (MV))

The measurement was carried out by holding a 2g sample heated at a measurement temperature (380 ℃) for 5 minutes at the above temperature under a load of 0.7MPa using a flow tester (manufactured by Shimadzu corporation) and a mold of 2 φ -8L according to ASTM D1238.

(amount of modification)

The measurement was carried out by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer.

(melting Point)

The temperature was determined as the temperature corresponding to the maximum value in the heat of fusion curve when the temperature was raised at a rate of 10 ℃/min by a differential scanning calorimeter [ DSC ].

(solid content concentration)

1g of the aqueous dispersion was dried in a forced air dryer at 150 ℃ for 60 minutes, and the ratio of the mass of the heated residue to the mass (1 g) of the aqueous dispersion was expressed as a percentage, and this value was used as the solid content concentration of the aqueous dispersion before concentration obtained by polymerization.

Further, 1g of the aqueous dispersion was dried in a forced air dryer at 380 ℃ for 60 minutes, and the ratio of the mass of the heated residue to the mass (1 g) of the aqueous dispersion was expressed in percentage and used as the solid content concentration of the aqueous fluoropolymer dispersion after concentration.

(melt flow Rate (MFR))

The MFR is measured by a method according to ASTM D1238 under a load (e.g., 5kg in the case of PFA, FEP and ETFE) at a measurement temperature (e.g., 372 ℃ in the case of PFA or FEP and 297 ℃ in the case of ETFE) determined according to the kind of the fluoropolymer.

(evaluation of Dispersion stability)

(storage stability test)

30g of the aqueous fluoropolymer dispersion kept at 25 ℃ was placed in a dedicated vessel and kept at 5000rpm for 5 minutes by a centrifuge (himac CT 15D) made by Hitachi engineering Co., ltd, equipped with an RT15A7 type rotor, to separate the aqueous fluoropolymer dispersion layer from the sediment layer. The aqueous fluoropolymer dispersion layer was taken out to determine the amount of solid content, and the amount of sediment was calculated from the difference between the amount of solid content and the amount of solid content in the aqueous fluoropolymer dispersion used. The amount of the sediment was measured as a ratio (% by mass) of the amount of the fluoropolymer contained in the aqueous fluoropolymer dispersion to be used. The lower the ratio, the more excellent the storage stability.

(mechanical stability test)

100g of an aqueous fluoropolymer dispersion kept at 65 ℃ was circulated for 2 hours at a discharge flow rate of 10L/hr by a quantitative liquid feeding pump (RP-2000 type roller pump) made by Tokyo physical and chemical instruments Co., ltd., having a tube (Tygon tube) with an inner diameter of 4.76mm and an outer diameter of 7.94 mm. Thereafter, the amount of the sieve in the case of filtration with a 200-mesh SUS mesh was measured as the ratio (% by mass) of the amount of the fluoropolymer contained in the aqueous fluoropolymer dispersion to be used. The lower the ratio, the more excellent the mechanical stability.

(example 1)

A glass reactor having an internal volume of 1 liter and equipped with a stirrer was charged with 530g of deionized water, 30g of paraffin wax and 55.0g of ammonium perfluorohexanoate dispersant (APFH). Next, the contents of the reactor were heated to 85 ℃ and purged with TFE monomer to remove oxygen from the reactor. Thereafter, 0.03g of ethane gas was fed into the reactor, and the contents were stirred at 540 rpm. TFE monomer was added to the reactor until a pressure of 0.73MPaG was reached. 0.11g of Ammonium Persulfate (APS) initiator dissolved in 20g of deionized water was injected into the reactor at a pressure of 0.83 MPaG. After the initiator injection, a pressure drop occurred and the start of polymerization was observed. TFE monomer was added to the reactor to maintain the pressure and polymerization was continued until about 140g of TFE monomer had reacted. Thereafter, the inside of the reactor was vented until the pressure reached normal pressure, and the contents were taken out from the reactor and cooled. The supernatant paraffin wax was removed from the aqueous PTFE dispersion.

The solid content concentration of the obtained PTFE aqueous dispersion was 20.5 mass%, and the volume average particle diameter was 0.9nm.

A part of the obtained PTFE aqueous dispersion was put into a freezer and frozen. The frozen aqueous dispersion of PTFE was allowed to stand until 25 ℃ was reached to give a coagulated powder. The coagulated wet powder was dried at 150 ℃ for 18 hours. The melt viscosity of the PTFE powder at this time was 3.0X 10 ³ Pa.S, melting point 327.0 ℃.

The obtained PTFE aqueous dispersion was added with deionized water so that the solid content concentration reached 5.0 mass%, and the storage stability was evaluated, with the result that the amount of sediment was 0.1 mass%.

The same dispersant APFH as used in the polymerization was added to the obtained PTFE aqueous dispersion so that the amount of the dispersant became 10.0 mass%. Further, deionized water was added so that the solid content concentration reached 5.0 mass%, and the mechanical stability was evaluated, with the result that the sieve content was 0.1 mass%.

Further, 2.0g of a surfactant (Noigen TDS-80, manufactured by first Industrial pharmaceutical Co., ltd.) was added to 100g of the obtained aqueous PTFE dispersion, and the mixture was uniformly mixed and passed through a column packed with an anion exchange resin (product name: amberlite IRA900J, manufactured by Rohm and Haas). The resulting aqueous dispersion was maintained at 60 ℃ and the resulting concentrated phase was recovered by phase separation. The solid content concentration of the concentrated phase was 63 mass%. Further, water and a surfactant were added to adjust the solid content concentration to 60 mass% and the surfactant amount to 8 mass%, and the pH was adjusted to 9.6 with aqueous ammonia.

(example 2)

Polymerization was carried out in the same manner as in example 1 except that the polymerization temperature of 85 ℃ in example 1 was changed to 70 ℃.

(example 3)

Polymerization was carried out in the same manner as in example 1 except that 0.11g of Ammonium Persulfate (APS) initiator in example 1 was changed to 0.006 g.

(example 4)

Polymerization was carried out in the same manner as in example 1 except that 0.11g of Ammonium Persulfate (APS) initiator in example 1 was changed to 0.003 g.

(example 5)

Polymerization was carried out in the same manner as in example 1 except that 0.11g of Ammonium Persulfate (APS) initiator in example 1 was changed to 0.028 g.

(example 6)

Polymerization was carried out in the same manner as in example 1 except that 0.11g of Ammonium Persulfate (APS) initiator in example 1 was changed to 0.006g, and polymerization was continued until about 185g of TFE monomer was reacted.

(example 7)

Polymerization was carried out in the same manner as in example 1 except that 0.11g of Ammonium Persulfate (APS) initiator and 55.0g of ammonium perfluorohexanoate dispersing Agent (APFH) in example 1 were changed to 0.006g and that about 10g of TFE monomer was reacted until completion of the polymerization.

(example 8)

Polymerization was carried out in the same manner as in example 1 except that 0.11g of Ammonium Persulfate (APS) initiator in example 1 was changed to 0.006g, 0.03g of ethane gas was changed to 0.01g, the reactor pressure at which 0.83MPaG was maintained was changed to 0.20MPaG, and polymerization was continued until about 40g of TFE monomer was reacted.

(example 9)

0.11g of Ammonium Persulfate (APS) initiator in example 1 was made 0.006g, 55.0g of ammonium perfluorohexanoate dispersant (APFH) were brought to 22.0g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy ] propoxy group]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 1 except that the polymerization was continued until about 40g of TFE monomer was reacted.

(example 10)

Except that 22.0g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy ] group in example 9 was used]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 9 except that the amount was changed to 16.5 g.

(example 11)

Except that 22.0g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy group in example 9 was used]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 9 except that the amount was changed to 11.0 g.

(example 12)

Except that 22.0g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy ] group in example 9 was used]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 9 except that the amount was changed to 9.9 g.

(example 13)

22.0g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy ] group as in example 9 was added]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 9 except that 110.0g of ammonium perfluorovalerate dispersant (APFP) was used, and polymerization was continued until about 140g of TFE monomer was reacted.

(example 14)

A glass reactor having an internal volume of 1 liter and equipped with a stirrer was charged with 530g of deionized water, 30g of paraffin wax and 55.0g of ammonium perfluorohexanoate dispersant (APFH). Next, the contents of the reactor were heated to 85 ℃ and purged with TFE monomer to remove oxygen from the reactor. Thereafter, 0.03g of ethane gas and 1.12g of perfluoro [3- (1-methyl-2-vinyloxy-ethoxy) propionitrile ] (hereinafter abbreviated as CNVE) were fed into the reactor, and the contents were stirred at 540 rpm. TFE monomer was added to the reactor until a pressure of 0.73MPaG was reached. 0.11g of Ammonium Persulfate (APS) initiator dissolved in 20g of deionized water was injected into the reactor at a pressure of 0.83 MPaG. After the initiator injection, a pressure drop occurred and the start of polymerization was observed. TFE monomer was added to the reactor to maintain the pressure and polymerization was continued until about 140g of TFE monomer had reacted. Thereafter, the inside of the reactor was vented until the pressure reached normal pressure, and the contents were taken out from the reactor and cooled. The supernatant paraffin wax was removed from the aqueous PTFE dispersion.

The solid content concentration of the obtained PTFE aqueous dispersion was 19.9 mass%, and the volume average particle diameter was 1.3nm.

The obtained PTFE aqueous dispersion was put into a freezer and frozen. The frozen aqueous dispersion of PTFE was allowed to stand until 25 ℃ was reached to give a coagulated powder. The solidified wet powder was dried under vacuum at 70 ℃ for 50 hours. The PTFE powder in this case hardly flowed even when heated, and the melt viscosity could not be measured. The melting point was 327.0 ℃ and the CNVE modification amount was 0.20 mol%.

(example 15)

Polymerization was carried out in the same manner as in example 14 except that 0.03g of ethane gas in example 14 was not added.

(example 16)

Polymerization was carried out in the same manner as in example 14, except that the polymerization temperature of 85 ℃ in example 14 was changed to 70 ℃.

(example 17)

(example 18)

Polymerization was carried out in the same manner as in example 14 except that 0.11g of Ammonium Persulfate (APS) initiator in example 14 was changed to 0.006g, 1.12g of CNVE was changed to 0.20g of HFP, and 0.03g of ethane gas was not added.

(example 19)

Polymerization was carried out in the same manner as in example 14 except that 0.11g of Ammonium Persulfate (APS) initiator in example 14 was changed to 0.006g, 1.12g of CNVE was changed to 0.12g of PMVE, and no ethane gas was added thereto in an amount of 0.03g until completion of the reaction of about 40g of TFE monomer.

(example 20)

Polymerization was carried out in the same manner as in example 19, except that 0.12g of PMVE in example 19 was changed to 0.46g of PPVE.

(example 21)

Polymerization was carried out in the same manner as in example 19, except that 0.12g of PMVE in example 19 was changed to 0.18g of CTFE.

(example 22)

Polymerization was carried out in the same manner as in example 19 except that 0.12g of PMVE in example 19 was changed to 0.01g, and the reactor pressure at which 0.83MPaG was maintained was changed to 0.20 MPaG.

(example 23)

Except that 55.0g of ammonium perfluorohexanoate dispersant (APFH) in example 16 was made 27.5g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy ] propoxy]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 16.

(example 24)

Polymerization was carried out in the same manner as in example 14 except that 1.12g of CNVE in example 14 was changed to 8.80g of PPVE, and polymerization was continued until about 120g of TFE monomer was reacted.

The aqueous PFA dispersion thus obtained had a solid content concentration of 18.5% by mass and a volume-average particle diameter of 6.0nm.

A part of the aqueous PFA dispersion obtained was put into a freezer and frozen. The frozen aqueous PFA dispersion was allowed to stand until 25 ℃ was reached, yielding a coagulated powder. The coagulated wet powder was dried at 150 ℃ for 18 hours. The PFA powder at this time had a melt flow rate of 230g/10 min, a melting point of 319.7 ℃ and a PPVE modification amount of 1.49 mol%.

(example 25)

Polymerization was carried out in the same manner as in example 24 except that 8.80g of PPVE in example 24 was changed to 5.90g and 0.03g of ethane gas was changed to 0.02 g.

Comparative example 1

Except that 22.0g of 2, 3-tetrafluoro-2- [1, 2, 3-hexafluoro-2- (trifluoromethoxy) propoxy group in example 9 was used]Ammonium propionate dispersant (CF) ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COONH ₄ )[PMPA]Polymerization was carried out in the same manner as in example 9 except that the amount was changed to 8.3 g.

The solid content concentration of the obtained aqueous PTFE dispersion was 7.1% by mass, and the volume average particle diameter was 121.6nm.

The dispersion stability of the obtained PTFE aqueous dispersion was evaluated, and as a result, the mechanical stability and storage stability were low, and the dispersion stability was insufficient.

The polymerization conditions in each example and the evaluation results of the resulting aqueous fluoropolymer dispersion are shown in tables 1 and 2, respectively.

[ TABLE 1 ]

[ TABLE 2 ]

Note) was performed in example 7 at a solid content concentration of 1.0 mass%.

Industrial applicability

According to the method for producing an aqueous fluoropolymer dispersion of the present invention, an aqueous dispersion containing fluoropolymer particles having an extremely small particle diameter and having excellent dispersion stability can be produced without using a long-chain fluorosurfactant. The aqueous fluoropolymer dispersion obtained by the production method of the present invention and the fluoropolymer fine powder obtained from the aqueous dispersion can be suitably used as additives for various molding materials, paints, cosmetics, waxes, greases, toners, and the like; electrode binders for secondary batteries or fuel cells, hardness modifiers for electrode binders, water repellent agents for electrode surfaces, and the like.

Claims

1. A process for producing an aqueous fluoropolymer dispersion, which comprises polymerizing a fluoromonomer in an aqueous medium in the presence of a fluorinated surfactant having a LogPOW of 3.4 or less and a polymerization initiator, wherein the aqueous dispersion contains at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene and a melt-processable fluororesin other than polytetrafluoroethylene,

the melt-processable fluororesin is a tetrafluoroethylene/perfluoro (alkyl vinyl ether) copolymer,

the polymerization is carried out in the presence of a chain transfer agent in an amount of 159ppm to 3000ppm relative to the total amount of the fluorine-containing monomer supplied; and/or the polymerization is carried out in the presence of a modifying monomer in an amount to give a fluoropolymer having a modified monomer unit content in the range of 0.02 to 1.49 mol%,

the chain transfer agent is ethane or propane,

the modified monomer is selected from CF ₂ ＝CFORf ⁹ CN, at least one of fluorine-containing vinyl ether having a nitrile group, hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, perfluorobutyl ethylene, perfluorohexyl ethylene, and ethylene, wherein Rf ⁹ Represents an alkylene group having 2 to 7 carbon atoms into which an oxygen atom may be inserted between two carbon atoms,

in the case where the modifying monomer is the fluorine-containing vinyl ether having a nitrile group, the polymerization is carried out in the presence of the chain transfer agent,

the amount of the fluorine-containing surfactant in the aqueous medium is equivalent to 23000ppm to 500000ppm,

the fluorine-containing polymer is a particle having a volume average particle diameter of 0.1nm or more and 10nm or less.

2. The method for producing an aqueous fluoropolymer dispersion according to claim 1, wherein the fluorinated surfactant is a fluorinated compound represented by the following general formula (1),

X-(CF ₂ ) _m1 -Y (1)

wherein X represents H or F, m1 represents an integer of 3 to 5, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ M represents H or NH ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms.

3. The method for producing an aqueous fluoropolymer dispersion according to claim 1 or 2, wherein the polymerization is carried out in the absence of a fluorine-containing compound represented by the following general formula (2),

X-(CF ₂ ) _m2 -Y (2)

wherein X represents H or F, m2 represents an integer of 6 or more, and Y represents-SO ₃ M、-SO ₄ M、-SO ₃ R、-SO ₄ R、-COOM、-PO ₃ M ₂ 、-PO ₄ M ₂ M represents H, NH ₄ Or an alkali metal, R represents an alkyl group having 1 to 12 carbon atoms.

4. The method for producing an aqueous fluoropolymer dispersion according to claim 1 or 2, wherein the polymerization initiator is at least one selected from the group consisting of persulfates and organic peroxides.

5. The method for producing an aqueous fluoropolymer dispersion according to claim 1 or 2, wherein the amount of the polymerization initiator is 1ppm to 5000ppm in the aqueous medium.